PREPLANNING BUILDING HAZARDS
BY FRANCIS L. BRANNIGAN, SFPE
Editor`s note: For further reference, consult Building Construction for the Fire Service, Third Edition. Page numbers are included after each caption for your convenience.
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(Top) These heavy wood trusses in an Orlando, Florida, clubhouse restaurant might appear to be able to withstand fire for some time, but note that they are carried on an unprotected steel beam that is supported on unprotected steel columns. Not apparent in the slide is the totally combustible restaurant environment and the fact that exterior streams can be directed only through windows on one side with no safe distance between the building and the lake. Always determine the vulnerability of the total path the load must take to reach the earth. (Ref. p. 78).
(Upper middle) The wood and steel industries are competitors. The wood industry points out quite rightly that the huge laminated wooden beam, seen here, will simply char in most fires and retain its strength. Firefighters, however, must look at the entire structure. Note that the wooden beam is almost universally supported on unprotected steel columns, as shown here, which will fail at 1,100°F. Note also the lightweight wood and tubular steel trusses supporting a plywood roof. They can fail so fast that there may not be any softening of tar on the roof or other sign of imminent collapse.
(Lower middle) This is a closeup of a typical tubular steel wood truss. Two tubes meet within the wooden top or bottom chords. Wood, which would protect the steel from heat for a time, is removed. A steel pin carries heat to the interior of the connection, attacking the wood by pyrolytic decomposition (burning without flame). The result is rapid failure–particularly of the bottom chord, which is under tension. Tests at the University of Illinois showed failure in six minutes. (Ref. pp. 541-542).
(Bottom) Typical fire failures of tubular steel wood trusses. (Ref. pp. 529-530).
FRANCIS L. BRANNIGAN, SFPE, a 55-year veteran of the fire service, began his fire service career as a naval firefighting officer in World War II. He`s best known for his seminars and writing on firefighter safety and for his book Building Construction for the Fire Service, Third Edition, published by the National Fire Protection Association. Brannigan is an editorial advisory board member of Fire Engineering.
